Previous pocketed coil spring assemblies include a number of discrete coil springs, each of which is enclosed in a fabric pocket in a length of folded fabric material. Longitudinal axes of the spring coils are generally parallel with one another so that the top and bottom end turns of the coil springs define top and bottom faces of the spring unit. These spring assemblies can be fabricated by forming rows of the pocketed coil springs and binding or adhering the individual rows together.
Individual pocketed springs are typically secured to adjacent pocketed springs by an adhesive, an ultrasonic weld, or a mechanical fastener near the top or over substantial portion of the longitudinal axes of the joined springs. However, these fastening techniques cause shearing force within the fabric pockets, which reduce the freedom of movement of individual coils when the coils are compressed. This influences the vertical restoring force of the coil springs, thereby interfering with mechanical equilibrium of the mattress. Furthermore, these fastening techniques can add cost and complexity to the manufacture of a coil spring assembly.
Therefore, there is a need for an improved pocketed coil spring mattress assembly.